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Power supply and related systems and methodsPower supply and related systems and methods description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060227581, Power supply and related systems and methods. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND [0002] Thermal batteries are often used to power the circuitry in certain devices, such as missiles. Specifically, after activation, the battery powers, e.g., the electronic control circuitry and the motors that steer the missile. [0003] A thermal battery is activated by igniting an internal portion of the battery. Upon ignition, the battery commences current and voltage production. [0004] But unfortunately, upon activation, a thermal battery has a high equivalent series resistance (ESR)--typically on the order of tens of giga-ohms--which reduces the voltage level that the battery is able to generate across a load. Although the ESR reduces to a suitable value within a time typically on the order of 1/4 to 3/4 seconds, if the circuitry activates before the ESR is low enough--typically less than one ohm--and, thus, the output voltage high enough, the circuitry may initialize in an undesirable state or may otherwise malfunction. And if the circuitry malfunctions, it may cause a malfunction in the device, e.g., a missile, that incorporates the circuitry. [0005] FIG. 1 is a schematic block diagram of a conventional device 10, vehicle, such as a missile, having at least one load, such as a motor 20 and electronic circuitry 30, and a power source 35, including a thermal battery 40 with associated ESR 50. The motor 20 and electronic circuitry 30 are coupled to and receive a supply voltage Vs from the battery 40 via conductors 60 and 62. The assembly for igniting the battery is omitted for clarity. [0006] Typically, the electronic circuitry 30 operates in a reset mode when the supply voltage Vs is between a minimum operational level and a reset level, e.g., 0.5 Volts (V), and is fully operational when Vs is greater than the reset level. But if while the circuitry 30 is fully operational Vs falls below the reset level, then the circuitry re-enters the reset mode. Unfortunately, the circuitry 30 re-entering the reset mode may delay the start-up time for the missile 10, or may cause the missile to malfunction. [0007] More specifically, upon activation at missile-launch time, the battery 40 begins providing the supply voltage Vs to the motor 20 and electronic circuitry 30, which typically requires minimal current (on the order of a few milliamps) to reset itself, exit the reset mode, and perform, for example, pre-launch system checks. Consequently, because the circuitry 30 presents a relatively small load to the battery 40, Vs typically exceeds the circuitry's reset level relatively quickly, thus allowing the circuitry to become fully operational and perform the pre-launch routine within a few milliseconds after the battery 40 is activated. However, the motor 20, when operating, draws a relatively large amount of current on the order of 10 Amps, and thus presents a relatively large load to the battery 40. Therefore, if the circuitry 30 activates the motor 20 before the ESR 50 has fallen to a suitably small value, then the load presented by the motor 20 may cause Vs to fall below the reset level of the circuitry 30, which, as discussed above, causes the circuitry 30 to re-enters its reset mode. Unfortunately, the circuitry 30 re-entering its reset mode may undesirably delay or abort the launch of the missile 10. SUMMARY [0008] In an embodiment of the invention, a power supply includes a power source having first and second terminals. A circuit is coupled to the source and is operable to maintain a first quantity between the terminals within a predetermined range of values until a second quantity between the terminals has a predetermined value. [0009] Such a power supply provides the ability to delay activating a load until the current that the supply can provide is at a level acceptable for proper load function. BRIEF DESCRIPTION OF THE DRAWINGS [0010] FIG. 1 is a schematic block diagram of a conventional device; and [0011] FIG. 2 is a schematic view of a device according to an embodiment of the invention. DETAILED DESCRIPTION [0012] FIG. 2 is a schematic block diagram of a device 100, such as a missile, which, according to an embodiment of the invention, includes a motor 110, electronic control circuitry 120, and a power supply 130 that includes a power source 140, such as a thermal battery with associated ESR 150, and a supply-activation circuit 160 such as a fuse. The motor 110 and electronic control circuitry 120 are coupled to and receive a supply voltage Vs from the power supply 130 via conductors 170 and 172. [0013] The supply-activation circuit 160 prohibits Vs from increasing above the reset voltage level of the control circuitry 120 until the ESR 150 reduces to a value ESRdesired that is low enough to allow the supply 130 to maintain Vs above the reset level while powering the control circuitry, the motor 110, and any other load coupled to Vs. According to Kirchov's voltage and current laws: Vs=R160/(ESR+R160) (1) I=Vi/(ESR+R160) (2) [0014] where Vi is the internal voltage of the battery 140 and R160 is the equivalent resistance of the circuit 160 and is small enough, e.g., often less than an ohm, such that the impedances presented by the control circuitry 120 and the motor 110 can be ignored. As the value of ESR 150 falls toward ESRdesired after the activation of the battery 140, Vs and I both increase until: Vs.sub.activate=R160/(ESR.sub.desired+R.sub.160) (3) I.sub.activate=Vi/(ESR.sub.desired+R.sub.160) (4) [0015] Because Vi, ESRdesired, and R160 are known quantities, then Iactivate and Vsactivate are also known. [0016] Consequently, the circuit 160 is designed to transistion from a relatively low impedance to a relatively high impedance, e.g., on the order of Megaohms or Gigaohms, in response to I=Iactivate and/or Vs=Vactivate per equations (3) and (4). [0017] For example, the circuit 160 may be a fuse designed to blow when the current through it equals Iactivate. Before the fuse blows, Vs has a level on the order of 0 V to a few hundred mV. Once the fuse blows, the value of ESR 150 is low enough such that Vs becomes greater than the reset voltage level of the circuitry 120 and remains greater than the reset voltage level even after the motor 110 is activated. Consequently, the circuitry 120 is significantly less likely to re-enter its reset mode when the motor 110 is activated, thus reducing the chances that the circuitry will delay or abort the launch of the missile 10. [0018] Still referring to FIG. 2, the operation of the missile 10 during a launch sequence is discussed where the circuit 160 is a fuse. [0019] First, an igniter (omitted from FIG. 2 for clarity) activates the battery 140. Because the fuse 160 is electrically closed, Vs.about.0 V. If Vs is large enough to power the circuitry 120 in its reset mode, then the circuitry 120 resets itself. If Vs is not large enough, then the circuity 120 is inactive. [0020] Next, the value of the ESR 150 begins decreasing while the fuse 160 remains electrically closed and Vs remains .about.0 V. Continue reading about Power supply and related systems and methods... Full patent description for Power supply and related systems and methods Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Power supply and related systems and methods patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Power supply and related systems and methods or other areas of interest. ### Previous Patent Application: Programmable power supply Next Patent Application: Rectifier for reducing current harmonics from unbalanced source Industry Class: Electric power conversion systems ### FreshPatents.com Support Thank you for viewing the Power supply and related systems and methods patent info. 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